This invention relates to an automatic temperature control system for a textile tenter frame apparatus.
In the operation of a textile tenter frame, the fabric within the tenter housing is heated to remove moisture. It is also necessary to bring the fabric (particularly synthetic fabrics) to predetermined temperature level for a period of time that will cause the fabric fibers to "set" in an essentially non-shrinkable state. With regard to this heat set temperature, the process of heating the fabric is initially one of driving the water from the fabric in a first heating zone within the frame, then elevating the fabric temperature in a second heating zone to the desired heat set temperature. Because of the typical moisture level in the fabric as it enters the tenter frame (usually from 20% to 40%) and the relationship of the specific heat and heat of vaporization of water as compared to the fabric specific heat, the major portion of heat energy is consumed in driving the water out of the fabric and accordingly the ultimate temperature of the fabric is heavily influenced by the moisture level of the fabric entering the tenter frame. This initial moisture level is caused by a number of factors such as knitting style, yarn surface quality, present water chemistry affecting surface tension and operation of the mechanical means for removing some of the water prior to tenter frame entry such as squeeze roll or a vacuum slot.
Prior to the present invention, the operator of a tenter frame apparatus was required to select a speed which would provide the desired heat set temperature of the fabric within the frame. If the proper set temperature was not reached during the heat set operation, a non-stable fabric was produced which would shrink during the subsequent washing, drying and pressing operations of a finished garment. On the other hand, if the operator allowed excessive temperatures to occur within the tenter, the fabric became scorched and unusable. Thus the operator's problem was to operate the tenter frame at a slow enough speed to provide the proper heat set temperature for the fabric and yet at a fast enough speed to prevent scorching and also provide an optimum production rate. Heretofore, the operator's decision on tenter frame speed setting were based primarily on his own prior experience or on the feel or observation of the material at the exit end of the tenter. Such reliance on the operator's skill and expertise or lack of same was often inefficient and costly, particularly in larger scale textile manufacturing facilities. The present invention solves the aforesaid problem and removes the uncertainty of temperature control in a tenter frame apparatus while also providing for an optimum production rate from the tenter frame.